The behavioral functions of the hippocampal formation have proven difficult to determine. This neural region is of considerable clinical significance: hippocampal dysfunction causes a profound amnesia defect, while diminished hippocampal function, as seen in senescence, is often associated with cognitive disabilities. One recent suggestion, derived from neurophysiological studies of the hippocampus, and of the effects of damage in this system, is that it is involved in the construction of internal models of the external environment - cognitive maps. According to this view, cognitive maps control exploratory reactions to new situations, and provide the basis for learning about places in the environment. Predictions of cognitive map theory concerning these kinds of behavior will be assessed in both intact and brain damaged animals. These studies will address the twin long-term goals of: (1) understanding the function of the hippocampal formation; and (2) providing a neural basis for the analysis of cognitive abilities.